Most conventional detergent compositions contain mixtures of various detersive surfactants in order to remove a wide variety of soils and stains from surfaces. In particular, various anionic surfactants, especially the alkylbenzene sulfonates, have been employed to remove particulate soils, and various nonionic surfactants, especially the alkyl ethoxylates, have been used for removing greasy soils and stains. Mixtures of such anionic and nonionic surfactants are used in many modern detergent compositions. Unfortunately, many such surfactants are prepared mainly from petrochemical feedstocks.
Considerable attention has lately been directed to nonionic surfactants which can be prepared using mainly renewable resources, such as fatty acid esters and sugars. One such class of surfactants includes the polyhydroxy fatty acid amides. A combination of such amide surfactants with conventional anionic surfactants has also been studied.
It will be appreciated by the skilled chemist that the polyhydroxy fatty acid amides contain multiple hydroxyl groups which are susceptible to conversion into other substituent groups. If such substituent groups were to be anionic in character, the resulting materials would be anionic surfactants. Thus, using a single fatty acid ester/sugar/amine feedstock, it would be possible to prepare not only a polyhydroxy fatty acid amide class of nonionic surfactants, but also anionic surfactant analogs thereof. Thus, the desirable mixtures of nonionic/anionic surfactants would become available from mainly renewable, nonpetrochemical feedstocks.
Sulfated derivatives of polyhydroxy fatty acid amides have been reported in the literature. These materials have been prepared by reacting chlorosulfonic acid or sulfuric acid plus urea with the hydroxyl constituents present in the polyhydroxy fatty acid raw material. However, it has now been determined that the preparation of such sulfated materials with polyhydroxy fatty acid amides using chlorosulfonic acid is non-routine. More particularly, yields of polyhydroxy fatty acid amide sulfate can be as low as 16% using chlorosulfonic. The reason for the low yields is not readily apparent. While not intending to be limited by theory, it may be that the hydrogen chloride which results from the reaction of the hydroxyl substituents with the chlorosulfonic acid can somehow attack the sugar substituent in the polyhydroxy fatty acid amide, thereby reducing overall yields. In any event, while such low yields may be tolerable under situations where a high priced ingredient is being prepared and wherein extensive purification procedures are justified, such is not the case when preparing low cost bulk items such as detersive surfactants.
By the present invention, an improved method for sulfating polyhydroxy fatty acid amides has been devised which uses sulfur trioxide in the form of a pyridine complex. Overall conversion of the polyhydroxy fatty acid amide into the sulfated polyhydroxy fatty acid amide is substantially increased.